1. Field of the Invention
The present invention relates to an expandable tubular reinforcing member used for a body lumen, such as a blood vessel, for reinforcement, and more particularly to a flexible stent that can be inserted into a body lumen describing a tortuous path and moved to a body cavity where it can be expanded in situ in both the radial and circumferential directions.
2. Description of the Prior Art
The art is quite developed concerning stents for the purpose of reinforcing a weakened body lumen to prevent collapse and occlusion of the fluid passageway defined by the body lumen. As is known, expandable stents are inserted in such body lumens using balloon catheters in a technique known as angioplasty. The stent, usually of tubular cylindrical form, must have an initial diameter that is suitable for insertion through a body lumen and into the targeted body cavity, but must be expandable in the radial and circumferential directions to support a cavity wall to maintain the patency thereof, and the radial strength to support and maintain this capability. Although such stents are in general known, nevertheless, the need for an improved design remains a goal to be sought. The continuing need for a flexible stent, that effectively can be inserted through narrow tortuous passageways of the body into a target body cavity, and which will have the requisite radial strength and support capability in the circumferential direction, still exists.
Accordingly, it is an object of the present invention to provide a flexible stent that has excellent flexibility to allow it to be inserted into a body lumen and advanced in an axial direction through narrow tortuous passageways, and to have the requisite radial strength and support capability in the circumferential direction to maintain the patency of the body cavity in which it is inserted.
It is a further object of the present invention to provide a flexible stent that is readily expandable by a balloon catheter in radial and circumferential directions.
The foregoing objects of the invention are achieved by a novel design for a stent that employs a unique mesh configuration and cellular construction, and yet is simple to manufacture.
This is accomplished by providing an expandable tubular reinforcing member for use for a body lumen that comprises, a pair of end sections each constituted of an endless expandable element and having a preselected diameter, an elongated element of sinuous configuration defining a plurality of U-bends extending between the end sections and spaced therefrom and being disposed in a helical configuration of said preselected diameter with the turns of the helix being spaced apart, a plurality of first interconnecting strips, each having a bend, spanning the space between axially successive turns of the elongated element and interconnecting axially aligned proximate U-bends of the elongated element to define cells bounded by the elongated element and circumferentially successive first interconnecting strips, and a plurality of second interconnecting strips, each having a bend, spanning the spaces between the elongated element and the pair of end elements and interconnecting the proximate U-bends of the elongated element nearest to the end sections to define cells bounded by the end sections, the elongated element and circumferentially successive second connecting strips.
The U-bends of the elongate element of the expandable tubular reinforcing member have legs that are slightly splayed. Also, for the majority of the elongate element, one leg of the U-bend is longer than the other. However, for at least the first and last U-bends of the elongate element, the legs are of equal length. The expandable tubular reinforcing member has each end section characterized by a sinuous configuration defining a plurality of U-bends which are axially aligned with the proximate U-bends of the elongate element nearest to the end sections. In a preferred design, the expandable tubular reinforcing member is characterized by a pitch of the helix of the elongate element from about 20 to about 25 degrees.
In a more specific form, the expandable tubular reinforcing member used for a body lumen comprises, a pair of end sections each constituted of an endless element of sinuous configuration defining a plurality of U-bends and having a preselected diameter, an elongated element of sinuous configuration defining a plurality of U-bends extending between the end sections and spaced therefrom and being disposed in a helical configuration of said preselected diameter with the turns of the helix being spaced apart, the U-bends of the elongated element being substantially aligned with the U-bends of the end sections, a plurality of first interconnecting strips, each having a bend, spanning the space between axially successive turns of the elongated element and interconnecting axially aligned proximate U-bends of the elongated element to define cells bounded by the elongated element and circumferentially successive first interconnecting strips, and a plurality of second interconnecting strips, each having a bend, spanning the spaces between the elongated element and the pair of end elements and interconnecting axially aligned proximate U-bends of the end sections and the elongated element to define cells bounded by the end sections, the elongated element and circumferentially successive second connecting strips.
In a further development, the strips having bends which divide the cells also serve as common or shared boundaries between a cell and the next preceding cell in the circumferential direction and the next succeeding cell in the circumferential direction. Also, the U-bends of the elongate element act as common or shared boundaries between a cell and the cell next preceding in an axial sense and the cells next succeeding in an axial sense. In the cellular structure developed by the elongate element and the strips, cells in successive turns of the helix are offset by one-half cell in the circumferential direction.
Other and additional advantages and objects of the present invention will become more readily apparent from the following detailed description of a preferred embodiment of the invention when taken with the appended drawing.